Chemotherapy based on HPMA copolymer conjugates with pH-controlled release of doxorubicin triggers anti-tumor immunity.

A novel class of anti-cancer therapeutics - polymeric conjugates of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers and doxorubicin with pH-controlled release of the drug - is highly efficient in killing tumor cells in vitro and is potent in eradicating growing tumors in vivo. Moreover, in comparison with low-molecular-weight drugs, the macromolecular therapeutics show decreased acute as well as delayed adverse side-toxicity. More importantly, the polymeric conjugates trigger the onset of specific anti-tumor immune response and this anti-tumor immunity can be transferred with splenocytes to naïve recipients. In other terms, chemotherapy based on conjugates of HPMA copolymer with doxorubicin possesses immunomodulating properties. This finding might also have wider implications for the management of relapsing tumors in human patients.

Cytostatic and immunomobilizing activities of polymer-bound drugs: experimental and first clinical data.

An N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer carrier containing doxorubicin and human immunoglobulin as an actively/passively targeting moiety was used in four patients with generalized breast cancer resistant to standard cytotoxic chemotherapy. The dose and time schedule were deduced from a Phase I clinical trial in which doxorubicin bound to HPMA copolymer carrier (PK1) was tested. It was confirmed that the Dox-HPMA-HuIg conjugate is stable and doxorubicin remains in the peripheral blood with a small amount also in the urine, mostly in its polymer-bound form. More than 116 biochemical, immunological and hematological parameters were determined for blood samples taken from patients 24 h, 48 h, 72 h and 1 to 11 weeks after treatment. Depending on the patient, some parameters decreased permanently or temporarily to the normal level (CRP, C3, CA 72-4, beta(2)-microglobulin, ferritin, CEA, CA 125, CD4, CD8, CE19, CD16(+)56(+), leu, ery) and some moved markedly towards physiological values (AST, ALT, ALP, GMT, CA 15-3, NSE, AFP). While the number of peripheral blood reticulocytes was significantly decreased after treatment with the classical free drug, their number was not affected or was even elevated after treatment with Dox-HPMA-HuIg. Increased absolute numbers of CD16(+)56(+) and CD4(+) cells in the peripheral blood and activation of NK and LAK cells in all patients support data obtained in experimental animals, pointing to a dual, i.e. cytostatic and immunomobilizing character of Dox-HPMA conjugates containing a targeting immunoglobulin moiety.

HPMA-hydrogels containing cytostatic drugs. Kinetics of the drug release and in vivo efficacy.

This study proposes a strategy to generate new anticancer therapy using hydrogel-based drug delivery systems to improve drug bioavailability and increase the therapeutic efficacy. We have synthesized biodegradable hydrogels based on N-(2-hydroxypropyl)methacrylamide (HPMA) with prolonged drug release. Pharmacokinetic data from in vitro studies showed that the in vitro release of hydrophilic drugs (doxorubicin, vinblastine) from HPMA-hydrogels is affected mainly by drug diffusion and only partially by hydrogel degradation. The release of hydrophobic drugs (cyclosporine A, CsA) actually copies the process of degradation and therefore it is slower. Hydrogels with degradation time of 50 h released the doxorubicin over a period of at least 96 h after s.c. implantation. Drug concentration at pharmacologically active levels was maintained in the bloodstream over a period of at least 4 days, ranging between 0.1 and 1 microg/ml. The therapeutic potential of HPMA-hydrogels in vivo was studied in Bcl1 leukemia. HPMA-hydrogels containing DOX were significantly more effective in inhibition of Bcl1 leukemia in comparison with free DOX or non-targeted polymeric drug (PK1). The efficacy of therapeutic combination using unspecific, hydrogel-based therapy with specific, antibody-targeted therapy at late stages of Bcl1 leukemia was also tested. In contrast to application of DOX alone, a cocktail of DOX with CsA as a blocker of P-glycoprotein (Pgp) incorporated into HPMA-hydrogel blocked the proliferation of Pgp-overexpressing multidrug resistant cell lines in vitro by induction of apoptosis.